1. Field of the Invention
The present invention relates to an image removing method, and more particularly to an image removing method by which an image formed on an image support by a method such as electrophotographic recording, inkjet recording and thermal recording can be removed so that the image support can be reused. In addition, the present invention also relates to an image removing device, and an image forming apparatus which can produce an image having good fixability, wherein the image can be removed from the image support when heated.
2. Discussion of the Background
Currently, a huge amount of hard copies are produced to distribute information. In such hard copies, images are formed by an image forming method such as printing (e.g., relief printing and planograph), electrophotographic recording, inkjet recording and thermal recording, or a writing material such as crayons and marker pens. Among these images, toner images formed by electrophotographic recording have advantages in that various image supports can be used, running costs are low when plain paper is used as an image support, and images can be formed at a high speed.
However, as a result of production of such a huge amount of hard copies, a large amount of paper is consumed, resulting in destruction of environment due to deforestation.
In order to prevent destruction of environment, only a method in which papers having images thereon are recycled by removing the image forming materials from the papers and using the used papers for forming a recycle paper has been used. On the other hand, methods in which images formed on papers are removed by cleaning so that the papers are reused for image forming have been proposed recently. In particular, various image removing methods have been proposed for images produced by electrophotographic methods by which a relatively large amount of paper is consumed.
The image removing methods in the electrophotographic field are broadly classified into methods in which image supports (e.g., papers and overhead projection sheets) are improved to easily remove images thereon; methods in which image forming materials are improved to easily remove images thereon; and methods in which images are removed using a material such as image removing liquids or image removing members.
Specifically the following methods have been disclosed:    (a) methods in which a water-swelling material formed of a crosslinked hydrophilic resin is formed on a support as a water-swelling layer and images thereon are removed by wetting the water-swelling layer with water (disclosed in published unexamined Japanese patent applications Nos. (hereinafter referred to as JOPs) 07-311523, 06-222604 and 11-174709); and    (b) methods in which an erasable paper whose surface is subjected to a releasing treatment is used as a support so that toner images formed thereon are easily removed (disclosed in JOP 04-067043).
However, these methods have a disadvantage such that a special paper has to be used as an image support, and thereby the above-mentioned advantages of electrophotographic recording are lost.
In addition, the following methods have also been proposed:    (c) a toner constituted of a material which can be discolored by a photochemical method, such as cyanine dyes and ammonium salts of organic boric acid, is used as the image material (disclosed in Japanese patent No. 2960229);    (d) a toner including a degradable material such as biodegradable plastics and photodegradable plastics is used as the image material (disclosed in JOP 04-356086); and
However, these methods have disadvantages in that resin components in the discolored toner images remain on the surface of a support, and thereby the surface roughness of the support is seriously deteriorated compared to the original support (for the method (c)); the images have poor color reproducibility because limited materials are used for the toner (method (c)); and when biodegradable materials are used, it is impossible to perfectly remove toner images if a large amount of toner is adhered to an image support (method (d)).
In addition, the following methods have been proposed.    (e) methods in which a toner image including a resin is removed by an image removing liquid including a component which can swell the resin, wherein the hydroxyl value and acid value of the swelling resin are specified (JOP 08-146648), the surface area of the toner is specified (JOP 08-146650), and a hydrophilic particulate material is included as the resin (JOP 08-146647), and a surfactant is included in a toner to enhance the penetrating property of the image removing liquid into the toner (JOP 08-146649).
The methods (e) disclosed in JOPs 08-146647-146650 in which an image removing liquid including a component dissolving or swelling a resin included in the toner is used has the following drawbacks:    (1) it is not preferable in view of safety that the removing liquid includes a solvent dissolving or swelling a resin; and    (2) since papers serving as an image support absorb the removing liquid or are swelled by the removing liquid, the papers are stretched even after dried, and thereby a problem such as jamming occurs when the papers are reused.
The present inventors checked the releasing effect of the surfactant-including toner disclosed in JOP 08-146649 without using a removing liquid. As a result, the toner does not have a releasing function by itself, namely it is difficult to remove toner images by a dry method. This is because the toner images do not absorb the image removing liquid.
In addition, a proposal such that in order to weaken an interface between an image and an image support, a surfactant is included in the image forming material or the image support is made. Although it is possible to remove images by the method, the adhesion between the image removing member and the image is weak, and therefore the method cannot be practically used.
Specific examples of the methods in which images are removed using an image removing member include the following:    (f) a force is applied to an image and an image support using an image removing member such as brushes and removing blades;    (g) an image removing member is overlaid on an image and both are heated so that an adhesion force is provided therebetween, resulting in adhesion of the image to the image removing member;    (h) the adhesion between an image and an image support is weakened using an image removing liquid or the like and the image is removed by a directly or indirectly removing method. At this point, the direct removing method means that, for example, a toner image fixed on a paper support is scraped off, and the indirect removing method means that, for example, a toner image is transferred to an image removing member, and the image on the image removing member is scraped off.
When images are removed by a direct or indirect removing method without weakening the adhesion between the image and the support, it is difficult to perfectly remove the images. In this case, if the images are forcibly removed, the support is damaged, which is not preferable in view of reuse of the support.
The methods using an image removing liquid are preferable because of not damaging the support and the image removing rate can be dramatically improved. However, in the methods a shear force is caused between a paper support and a toner image by applying the image removing liquid to reduce the adhesion force therebetween. In this case, the paper support is swelled and therefore the paper support is stretched. Therefore, a problem such as paper jamming tends to occur when the paper support is reused. In addition, a solid toner image having a large area cannot be well removed because the resins included in toner images are typically insoluble in water or are not swelled by water. Therefore even an image removing liquid including a surfactant cannot penetrate into such a solid toner image, and thereby the solid toner image cannot be well removed. If a solid toner image on a support is dipped into an image removing liquid, the toner image is fairly removed, but the above-mentioned problem in that the paper support is swelled and therefore the paper support is stretched, resulting in occurrence of paper jamming occurs.
JOP 01-297294 discloses a method in which a thermofusible image removing material is contacted with an image formed on an image support using a thermofusible ink while applying heat thereto, and then a removing substrate is overlaid thereon followed by cooling, resulting in removal of the thermofusible ink image from the image support.
Japanese patent No. 2,584,112 (i.e., JOP 04-64472) discloses an eraser which is prepared by forming a thermofusible resin layer on a substrate and which can remove a toner image formed on an erasable paper by contacting the erasable paper while heating the thermofusible resin layer.
JOP 2000-267525 discloses an image forming material removing device which is prepared by forming an image removing layer consisting of a thermofusible resin on a substrate and which can remove an image forming material adhered to an image support by contacting the image removing layer with the image forming material upon application of heat thereto such that the image forming material adheres to the image removing layer.
However, these methods have a drawback in that the adhesive force between the image forming material and the image support is so strong that the image forming material is broken and thereby the image cannot be perfectly removed, or the image support is broken, and thereby the image support cannot be reused.
Because of these reasons, a need exists for an image removing method by which images on a paper support can be removed to reuse the image support without using an image removing liquid or the like.